Axion String Dynamics I: 2+1D

TL;DR

This paper introduces a new algorithm for simulating axion string dynamics in 2+1 dimensions, revealing that string core treatment significantly affects axion production efficiency, with implications for understanding axionic dark matter.

Contribution

The paper develops a novel algorithm for accurately modeling axion string cores in 2+1D, improving predictions of axion production and outlining extensions to 3+1D.

Findings

Axion production is about twice as efficient with full string tension.

String network behavior in 2+1D differs from 3+1D, affecting extrapolations.

New simulation method improves understanding of axion cosmology.

Abstract

If the axion exists and if the initial axion field value is uncorrelated at causally disconnected points, then it should be possible to predict the efficiency of cosmological axion production, relating the axionic dark matter density to the axion mass. The main obstacle to making this prediction is correctly treating the axion string cores. We develop a new algorithm for treating the axionic string cores correctly in 2+1 dimensions. When the axionic string cores are given their full physical string tension, axion production is about twice as efficient as in previous simulations. We argue that the string network in 2+1 dimensions should behave very differently than in 3+1 dimensions, so this result cannot be simply carried over to the physical case. We outline how to extend our method to 3+1D axion string dynamics.